The present invention relates to a new and improved apparatus for grinding gear teeth having an involute-shaped tooth flank profile, wherein to-and-fro generating movements are carried-out between a dished or plate-shaped grinding wheel and the gear teeth as well as feed or advance movements in the tooth lengthwise direction, adjustment or readjustment movements for compensation of the wear of the grinding wheel, and finally, indexing movements.
In the case of highly loaded gear teeth, as such for instance are employed in the aircraft industry, it is not only necessary to grind the involute-shaped tooth flanks, but also the tooth root or bottom land, so that there can be maintained prescribed tooth root clearances or fillets and to obtain a fine surface of the tooth base or bottom land. Both of these factors are extremely important in consideration of the permanent bending strength of the gear teeth.
With heretofore known methods of the previously described species and the state-of-the-art grinding machines provided for the performance of such method, such as for instance disclosed in German patent publication No. 2,726,843, and the corresponding U.S. Pat. No. 4,213,277, granted July 22, 1980, wherein such grinding machine is equipped with grinding wheel-dressing and readjustment devices, it is possible to grind in short machining times teeth flanks having great accuracy. However, it was not heretofore possible to machine the tooth root or bottom land, so that whenever there were demanded high requirements at the tooth root fillets and surface quality of the tooth bottom land, it was heretofore necessary to chuck or clamp the workpiece, prior to or following its machining at a tooth flank-grinding machine, upon a separate machine serving for machining the tooth root or bottom land.
There are indeed known to the art methods and apparatus for the form grinding of tooth flanks, wherein the profile or shape of the grinding wheel, continuously maintained by a dressing device, for instance as taught in German Pat. No. 2,536,895, and the corresponding U.S. Pat. No. 4,128,093, granted Dec. 5, 1978, is structured such that, apart from producing the involute-shape of the teeth flanks there are also realized the desired shape and surface quality of the bottom land or tooth root. During form or shape grinding it is however disadvantageous that the accuracy of the shape of the tooth flanks is dependent upon the accuracy of the profile or shape of the grinding wheel, so that when greater requirements are placed upon the quality of the gear teeth it is necessary to quite frequently reshape the grinding wheel. Hence, there is needed a complicated dressing device which is controlled by templets or a generating drive. Furthermore, there exists the well known difficulty that during form grinding of helical gearing, it is necessary to alter the profile of the grinding wheel with decreasing grinding wheel diameter. Moreover, in the case of form grinding, in contrast to indexing generating grinding, it is not possible to undertake random profile corrections at the teeth flanks. Finally, the machining times are extremely long during form grinding.